Spectrophotometric determination and removal of Rhodamine 6G from aqueous solutions using unfunctionalized multi-walled carbon nanotubes; with greenness and blueness assessment

This paper conducted a comprehensive study of the one-step removal of Rhodamine 6 G (Rh 6G) dye from aqueous solutions using unfunctionalized multi-walled carbon nanotubes (MWCNTs). Unfunctionalized MWCNTs were characterised using FT-IR, FESEM, EDX, and mapping, both before and after adsorption. A UV-Visible spectrophotometric method at λmax 525 nm was validated for Rh 6G quantification (1–12 mg/L), exhibiting excellent linearity (R2 = 0.998), high accuracy (101.417 ± 1.687), and low RSD (1.664%). The limits of detection (LOD) and quantification (LOQ) were 0.380 mg/L and 1.152 mg/L, respectively.The optimal removal of Rh 6G on an unfunctionalized MWCNTs were found at an initial dye concentration of (2 mg/L), pH 10 at 308 K under shaking time of 10 min, using (0.001 g) of MWCNTs. A pH 10 value affected the adsorption of Rh 6G dye onto unfunctionalized MWCNTs. In this study, adsorption isotherms are described using means of Langmuir, Freundlich,Tempkin and Sips isotherms. The results indicated the adsorption isotherm could be well described with Freundlich model. The thermodynamic constants of the adsorption of the dye on unfunctionalized MWCNTs were calculated; the values indicated that a spontaneous and endothermic process was occurred. Kinetic studies aligned with the pseudo-second-order model. Unfunctionalized MWCNTs exhibit promising properties as a low-cost, easily applicable, and sustainable adsorbent, eliminating the need for harmful acid treatments and offering rapid adsorption compared to other adsorbents. In this work, the suggested analytical UV-Visible spectrophotometer method was evaluated using new greenness and blueness assessment tools: GAPI, ComplexGAPI, MoGAPI, ComplexMoGAPI, and BAGI. These tools showed appropriate green and blue scores. The GAPI and MoGAPI tools exhibited seven green colour, while both ComplexGAPI and ComplexMoGAPI tools exhibited 14 green colours with a high yield of 90.02%. The high BAGI score of 75 confirms that this adsorption method was strong applicability.